Fiber type composition of the human quadratus plantae muscle: a comparison of the lateral and medial heads

Fiber type composition of contiguous palmaris longus and abductor pollicis brevis muscles: Morphological evidence of a functional synergy

The palmaris longus (PL) tendon is used in surgical opponensplasty to restore functional hand movements in thenar paralysis. Although successful PL autologous tendon transfer has been attributed to an established synergistic relationship between the PL and abductor pollicis brevis (APB) muscles in vivo, this functional relationship may be dependent on the quality of their spatial relationship and properties of their constituent muscle fibers. The purpose was to compare the proportion of type I and type II muscle fibers in the APB based on its contiguous morphological relationship with the PL tendon for indirect insight into their functional synergy, contractile capacity, and digastric arrangement. Twenty-four contiguous PL and APB specimens were harvested from the upper limbs (12 right and 12 left) of twelve formalin-embalmed cadavers (mean age: 74 ± 10 years). The fiber type composition of these muscles was determined by labeling serial cross sections with myosin heavy chain (MyHC) type I and type II monoclonal antibodies. The PL consisted of a relatively heterogeneous fiber type composition irrespective of the presence of a discrete (type I: 41 ± 11%; type II: 55 ± 12%; hybrid: 4 ± 3%) or rudimentary (type I: 49 ± 10%; type II: 45 ± 9%; hybrid: 6 ± 4%) tendinous connection with the APB. The APB fascicles arranged contiguously with the PL through a discrete tendon had significantly greater proportions of type II fibers (41 ± 19%) compared to those with rudimentary PL connections (type II: 15 ± 8%). Therefore, the APB fascicles arranged in a digastric relationship with the PL may have the capacity to produce more powerful contractions than those with rudimentary PL tendons based on the known contractile properties of type II muscle fibers. Knowledge of the spatial relationship between the PL and thenar musculature prior to PL autologous tendon transfer may be a useful indicator of the quality of established synergy in vivo.

Morphological characteristics and variations of the human quadratus plantae muscle

The quadratus plantae (QP) is a highly variable structure. A number of partly inexact descriptions of this entity have been provided in textbooks of anatomy. Although several authors have examined the QP, its exact site of origin and type of insertion have hitherto not been specified. The aim of this study has been to provide detailed qualitative and quantitative data about the number of heads, points of origin, and type of insertion of the QP. The QP in both feet of 50 formalin-fixed specimens of body donors (25 men and women) were analyzed by gross anatomical dissection. It was composed of one (34%), two (57%) or three heads (9%). The latter condition was observed only in men. The lateral head was absent in 31 feet, and the medial head only in one right foot of a man. The medial head arose, amongst others, in 100% of the examined cases from the medial calcaneal surface, in 93% from the long plantar ligament and in 80% from the plantar calcaneocuboid ligament. The lateral head arose, amongst others, from the long plantar ligament in 90%, and from the lateral process of the calcaneal tuberosity in 64% of the examined feet. The type of insertion was always a mixture of at least two of three types; i.e. muscular (84%), tendinous (89%) and aponeurotic (45%). As additional findings, the flexor digitorum accessorius longus (FDAL) and the peroneocalcaneus internus (PCI) were observed in 12% of all individuals and in 20% of men. The present investigation revealed that the QP may be classified according to the number of heads, but no classification can be given for its points of origin or type of insertion. The present data are mandatory for anatomical and surgical practice and will hopefully lead to further imaging and biomechanical studies.

Skeletal Muscle Microvasculature: A Highly Dynamic Lifeline

Skeletal muscle is highly irrigated by blood vessels. Beyond oxygen and nutrient supply, new vessel functions have been identified. This review presents vessel microanatomy and functions at tissue, cellular, and molecular levels. Mechanisms of vessel plasticity are described during skeletal muscle development and acute regeneration, and in physiological and pathological contexts.